The invention relates to a current source with multiple outputs for connecting an electrical load.
Regulated power supplies in the most varied of embodiments are known from the prior art, including dimmable embodiments, with which the output power can be set as desired. U.S. Pat. No. 7,659,673 B2 discloses e.g. a multi-channel current source for operating LED strings of various colours. Each of the LED strings has its own current regulator for regulating the current flowing through the particular string. Furthermore, a controllable switch that is controlled by means of a PWM signal, and with the aid of which the individual LED strings can be dimmed, is arranged in each of the LED strings.
Other DC current sources with multiple outputs are known from e.g. DE 10 2010 048 951 A1 by the applicant, from WO 2007/039862 A2 or EP 0 788 850 B1.
Dimmable DC current sources are often used for operating light systems that have many kinds of lights, in particular LEDs of different colours. By mixing the colours of the individual basic colours—in the RGB colour space these are red, green and blue—many visible colours can be displayed. To this end, it is necessary that the different outputs or channels of the DC current source may be dimmed independently of each other. As mentioned above, in the prior art there are a whole range of multi-channel DC current sources that have individually dimmable channels. However, with these current sources the problem emerges that, when the current in the individual channels increases or decreases, the colour location of the emitted light in the colour space also changes. The drifting of the colour location in the colour space is explained below by means of FIGS. 1a and 1b. 
FIG. 1a shows a CIE normal chromaticity diagram that represents all colours that can be perceived by an observer. In the middle of the CIE chromaticity diagram, the light emitted by the three colour spotlights is perceived as white, as the three basic colours are mixed in approximately equal measures. The segment 80 represented at the top right of the white area is shown again enlarged in FIG. 1b. 
In FIG. 1b, the colour location of a so-called XLamp, a special kind of LED from the Cree company, is shown depending on the current flowing through the LED. The operating current thereby lies between 175 mA and 2500 mA. As should be obvious, the colour location shifts with the current intensity and with it also the wavelength of the emitted light. Moreover, the colour temperature also shifts with the intensity of the constant current. Dimming of the LED therefore has the effect of changing the blue, red or green proportion of the emitted light, and the LED therefore has a perceptibly different colour tone depending on the dim setting. In a light system that is constructed in RGB technology, the constant current dimming of the LED effects a slight colour shift of the light perceived by the observer. This is undesirable for many applications.
From each of U.S. Pat. No. 8,044,609 B2, DE 10 2010 031 236 A1, US 2012/0200229 A1 and US 2006/0255753 A1 a current source with several outputs is known, which provides a constant current for operating an electrical load available on every output, wherein the individual outputs can be individually dimmed by means of a dedicated dimming device. If LEDs are connected to the outputs, however, dimming of the constant current again leads to a colour location shift of the light emitted by the LEDs.